During the polymerization of vinyl chloride to polyvinyl chloride under aqueous polymerization conditions, the entire amount of vinyl chloride is not converted quantitatively to polyvinyl chloride and a residual amount of vinyl chloride remains. This residual amount of vinyl chloride must be removed practically quantitatively from the aqueous polyvinyl chloride. Various methods have been suggested for this purpose; in particular, low vinyl chloride contents are achieved in the finished aqueous polyvinyl chloride after distilling off the vinyl chloride evaporating under a vacuum with the aid of a treatment with steam.
Special problems occur with coagulation-sensitive latices since high temperatures and high shearing load cause coagulation of the latices so that no usable product is obtained (further processing is practically impossible.) Therefore, the treatment with steam at elevated temperatures with agitation is difficult. Another problem is the large amount of foaming which occurs during the degasification. The use of anti-foaming agents has not been successful in this connection because the product quality is negatively affected by the anti-foaming agents, particularly if larger amounts have to be employed.
Heretofore, coagulation-sensitive latices could only be degased under extremely mild conditions in terms of temperature control, steam treatment, etc. But this means a great expenditure of time and frequently also unsatisfactory degasification values, that is, a high residual vinyl chloride content in the latex.